脆性材料压剪断裂方向影响因素的宏细观分析

Discussions on Fracture Factors of Brittle Materials under the Shear-Compression Condition

从物理学中摩擦力和固体力学应力状态的概念出发,讨论了脆性材料受压剪断时断裂面上摩擦力的存在性;基于脆性材料压剪宏观断裂形式和细观断裂机理,分析了影响脆性材料压剪断裂的主要因素。分析结果表明,脆性材料单压剪断时,起裂点上断裂面沿最大切应力方向,而试验中观察到宏观剪切面倾角大于45°。主要原因是,试验中试件端面附近存在摩擦力,且受压时坚硬晶粒楔入软介质,从而在材料内产生附加拉应力,改变了原有的单向压缩应力状态,也改变了后续断裂路径上的最大切应力方向。

Based on fundamental ideas in tribology and basic concept of stress state in solid mechanics,the existence of frictional force on shear plane is discussed under uniaxial compression of brittle materials.Based on macroscopic fracture forms and mesoscopic fracture mechanism,the key factors influencing shear fracture angle are analyzed.The main conclusions are as follows： when brittle materials are compressed and shear fracture occurs,shear fracture surface at the crack initiation point is consistent with the maximum shear stress.But the reason of shear fracture angle examined in experiment greater than 45° lies in that,frictional force between end face of test piece and pressure head of testing machine,and additional tensile stress produced in the materials when harder crystalline grain wedge in softer medium have changed original unidirectional compression stress state and the direction of maximum shear stress on next fracture path.